From: Carlos G Mendioroz (tron@huapi.ba.ar)
Date: Thu Oct 27 2005 - 16:29:06 GMT-3
Great, that's good but no good enogh.
Cisco used to have different MACs for differentiating BIDs, and now is
forcing the VLAN into the priority field just for that: unique BIDs.
If I wanted to have different roots, and granted that usually you do,
then you COULD modify ONE switch priority to do that.
But you COULD have the other with the same BID for both VLANS.
Questions is why you SHOULD have unique BIDs ...
Also, it is clear that BPDUs used at each VLAN space (if you accept the
abuse of notation :) are independent. I.e. switches are not going to
confuse different VLANs BIDs even if they happen to be the same value!
-Carlos
Feldman, Jim @ 27/10/2005 16:19 dixit:
> Carlos,
>
> I think the easiest what to understand this issue is through an example.
>
> Suppose you had 2 switches, A and B, and you also had 2 vlans, 1 and 2.
>
> Now, suppose you want to make Switch A the root bridge for vlan 1 and Switch
> B the root bridge for vlan 2.
>
> Without different BID's for each vlan, how would you do that?
>
> Jim
>
> -----Original Message-----
> From: Carlos G Mendioroz [mailto:tron@huapi.ba.ar]
> Sent: Thursday, October 27, 2005 3:15 PM
> To: ccielab@groupstudy.com
> Subject: OT: why many BIDs in PVST ?
>
>
> For those that are wondering, yes I'm reading the BCMSN courseware :)
>
> You know in STP there is a BID (Bridge ID) used to identify each
> participating bridge and its priority.
> Nowadays, also VLAN is used to make BIDs unique per VLAN, it used to be
> the case that switches had many MACs just for that.
>
> But, why do switches need different BIDs for different VLANs ?
>
>
-- Carlos G Mendioroz <tron@huapi.ba.ar> LW7 EQI Argentina
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